It is virtually impossible to keep a web server secret by not publishing any links to it. As soon as someone follows a link on your “secret” server to another server, your “secret” URL can be publically displayed in the reference tag of that other server’s reference protocol.
You have multiple options to stop United Data Collector from retrieving content from your website. One possibility is to use the robots.txt file to block access to the files and directories on your server, for example..